This invention relates to a flatbed image read system and in particular to an image read system for automatically extracting an original image.
A flatbed image reader for operating a read mechanism for an original placed on an document bed to read data enters widespread use. The flatbed image reader includes a one-dimensional image pickup device (line sensor) as a read  mechanism and reads reflected light from the original while moving (subscanning) a carriage on which the image pickup device and a light source are mounted relative to the original, thereby acquiring two-dimensional image information.
Some image read controllers for controlling an image reader include a function of automatically extracting the original portion from the read image and displaying the extracted original portion (automatic extraction function).
In the automatic extraction function, if the original is placed at an angle on the document bed, the inclination of the original placed on the document bed is corrected for display.
FIGS. 5A to 5D are drawings to show how a flatbed image reader reads the image of the original placed on an document bed. As shown in FIG. 5A, light applied from a line light source 113a mounted on a carriage 113 is reflected on an original 151 placed on an document bed 112 or an document bed cover 115 and enters a line sensor 113d through a reflecting mirror 113b and a lens 113c. 
Since the line light source 113a and the reflecting mirror 113b are not at the same position, light is applied to the read part in a slanting direction. Thus, in the positional relationship between the line light source 113a and the reflecting mirror 113b shown in FIG. 5A, a shadow of the size responsive to the thickness of the original 151 occurs in the outside portion of the original 151 to be read, particularly at the left of the figure (the lower side of the original) as shown in FIG. 5B. Since the shadow appears on the read image, an image read controller recognizes an image larger than the actual original as the area in which the original exists. Slight noise occurs in the surrounding portions of the original (FIG. 5C).
To remove the shadow and the noise from the original image, the image read controller including the automatic extraction function makes inclination correction to the area recognized as the original and then handles the image whose surrounding portions are cut as the image of the original.
At this time, the lower portion where the shadow occurs is cut larger than any other portion, as shown in FIG. 5D. For example, letting the lower cut width be a and the upper cut width and the left and right cut widths be c, b, and d respectively, a=2 mm and b=c=d=0.5 mm.
The shadow portion appearing on the image occurs because the position of the light source 113a and the read position do not match. Thus, if the original placed on the document bed is not inclined, the major portion of the shadow occurs along the base of the original image, as shown in FIG. 6. Thus, the lower cut width is increased, whereby the image of the original with the shadow and the noise removed can be acquired.
However, if the original is placed on the document bed on the skew, a shadow occurs on the skew across the base and one side of the original after inclination correction is made to the original. Thus, if the lower cut width is increased as in the related art, the shadow portion is contained in the original image on one side. The base portion is cut excessively and it is feared that a part may be missing from the original.